We propose to continue testing our original hypothesis that virus infections alter the surfaces of host cells causing them to be selectively susceptible to adhesion by potentially pathogenic bacteria. We have selected Staphylococcus aureus and human influenza A virus for continued study because staphylococcal pneumonia is a well-documented example of a life-threatening bacterial superinfection occurring in patients with complicated influenza. We have developed and refined an in vitro cell culture model system consisting of mammalian cell cultures, either unifected or infected with human prototype strains of influenza A virus, and incubated with [3H]S. aureus; this radioassay allows quantitation of staphylococcal binding to cell cultures and allows us to test potential receptor analogs for their ability to block binding. Our immediate aim is to further define staphylococcal 'adhesins' that mediate binding by comparing the outer membrane proteins of mutant, laboratory-adapted, and clinical strains of S. aureus using SDS-PAGE, autoradiography, and monoclonal antibodies. These strains, which demonstrate a wide variability of adhesion to virus-infected cells in vitro, will ultimately be tested in a mouse model to study and compare the early events after introduction of [3H]staphylococci into mice infected with influenza virus. We also propose to extend our work on characterization of the mammalian cell receptors that mediate binding using a 'Texas' blot procedure which we propose to develop, as well as, testing purified membrane components (from virus-infected cells) for their ability to block bacterial adhesion and to bind directly to S. aureus. Using basically the same approach we intend to characterize the membrane receptor for human fibrinogen which cross-links virus-infected cells and pyogenic cocci in vitro. Throat washes from adult subjects with and without influenza will be used to treat monolayers to determine any effects on subsequent bacterial adhesion. Ultimately we intend to use our in vivo radioassay mouse model to test the hypothesis that treatment of mice with receptor analogs, identified in the in vitro system, cna block or alter the course of bacterial superinfection.